(a) Field of the Invention
The present invention relates to a method for recycling alignment layer materials, more particularly to a method for recycling alignment layer material components of polyamic acids (sometimes referred to as xe2x80x9cPAAxe2x80x9d) and soluble polyimides (sometimes referred to as xe2x80x9csol. PIxe2x80x9d) by collecting alignment layer material waste solution massively produced in the LCD manufacturing process.
(b) Description of the Related Art
Liquid crystal responds differently to external forces such as electric fields according to the molecular arrangement. Therefore, the control of liquid crystal molecular alignment is very important for display component fabrication as well as for liquid crystal physical property research. However, it is difficult to obtain a uniform molecular arrangement by simply filling a gap between glass substrates with liquid crystal materials. Therefore, it is common to form an alignment layer on the glass substrate.
Although an alignment layer can be made primarily of inorganic or organic components and a mixture of both, organic materials are mainly used as a composition material of practical liquid crystal display components.
Since the introduction of SiO vacuum deposition suggested by Janning in 1972, the characteristics of liquid crystal materials have not been adversely affected by either the mass production of display components or the alignment control technology for liquid crystal display components. Hence an alignment control technology employing suitable organic polymers for mass production has been developed. Liquid crystal molecules are aligned by rubbing organic polymer layers formed on a glass substrate. The organic polymer layers are formed by a rotational coating method or a printing coating method, and then curing.
The rubbing method has been known since Mauguin observed in 1911 that the major axes of liquid crystal molecules become evenly aligned in a rubbed direction when glass substrates are rubbed in a certain direction by materials such as cloth, etc. Ever since then, despite the efforts devoted on the research for the rubbing methods and proper thin layer materials, a conclusive selection has not yet been made.
However, as high hydrolytic Schiff base liquid crystals are used since the beginning of the mass production of twisted nematic type LCD components, it has been essential that the glass frit sealing can secure the device reliability. Therefore, polyimide based materials were selected because it showed no problems in high temperature treatment. Thereafter, polyimide based materials have been proved to be superior to other organic polymers in all the aspects of printing, rubbing, alignment control, and chemical stability. Thus, polyimide based materials are widely used as alignment layer materials of various LCD components even today.
Generally, polyamic acids (PAA) or soluble polyimide (sol. PI) synthesize by reacting diamine and acid anhydride in a solvent. The printing material is polyamic acids or soluble polyimides, which become polyimide by drying, heating, and curing after printing.
The methods for forming an alignment layer using this polyimide include various methods such as spinning, spraying, dipping, printing methods, etc., as well as the printing method currently used most because of its compatibility with mass production processes.
However, the printing method has problems of high manufacturing costs because about 70% of the solution is wasted, i.e., not actually used in the alignment layer printing.
Additionally, treating waste alignment layer material also increases manufacturing costs.
Therefore, the present invention can reduce costs a lot by effectively recycling the waste alignment layer materials that are used in a liquid crystal display manufacturing process. Furthermore, it is an object of the present invention to provide a method for recycling the liquid crystal alignment layer materials that can reduce the waste disposal cost by remarkably decreasing the amount of the waste alignment layer materials.
The present invention provides a method for recycling alignment layer materials used for a liquid crystal display comprising steps of collecting waste solution of the alignment layer materials, solidifying polyamic acids and soluble polyimides by putting the above collected waste solution of alignment layer materials into an organic solvent or ultra purified water in which the alignment layer material constituents of polyamic acids and soluble polyimides are insoluble, and separating polyamic acids and soluble polyimides from the above organic solvent or ultra purified water in order to achieve the above object.